Safety cut-outs for electrically heated appliances



A. J. CHINN Apri! 26, 1955 SAFETY CUT-OUTS FOR ELECTRICALLY HEATED APPLIANCES Filed Sept. ,25, 1952 I F/G./.

United States Patent O SAFETY CUT-OUTS FOR ELECTRICALLY HEATED APPLIANCES Arthur J. Chinn, Slough, England, assignor to The Rheostatic Company Limited, Slough, England, a British company Application September 23, 1952, Serial No. 311,088

Claims priority, application Great Britain October 18, 1951 2 Claims. (Cl. 200-138) The invention relates to safety cut-outs for electrically heated appliances such as oil filled electric radiators in which an excessive temperature may be generated if a covering were placed over the radiator.

The switch on such a cut-out should remain closed when the radiator is running at its normal operating temperature and should carry the heater current indefinitely. It should not be tripped accidentally or by vibration but should trip when subject to excess ternperature, and should remain oil? until re-set by hand. It is desirable also that the cut-out should be located adjacent to the heater terminals and that it should occupy a minimum space. It is desirable also, that no special pockets or fittings should be required for the accommodation of the thermally sensitive element of the cut-out.

It is an object of the invention to provide a construction of cut-out affording such desiderata.

In the safety cut-out of the invention a magnet attracting one limb of a U-shaped armature carried on a flexible switch member gives contact pressure to the switch in closed position of the switch and retains the switch in open position magnetically by its attraction on the opposite limb of the armature in the tripped position of the switch.

An embodiment of the invention is illustrated in the accompanying drawing, in which Figure 1 is a vertical section partly in elevation of the improved cutout in set position;

Fig. 2 is a detail in perspective, and

Fig. 3, a section similar to Fig. 1 showing the switch in tripped position ready to be re-set.

Referring to Fig. l, a screwed stud 1 fixed in a base plate 2 carries a bimetal operating element 3 clamped between copper washers 4 and 5 adjacent to the base 2. The bimetal element thus has good heat conductive connection with the base of the switch which base is arranged with fixing holes for attachment of the switch to the surface of the radiator or heater to be protected. 2a indicates the cover of the cut-out.

Mounted on the stud 1 are the switch parts comprising a fixed contact plate 6, a spring switch lever designated generally by 7 and a magnet supporting plate 8 supporting a magnet 18. Above this plate is clamped a spring strip 9 on which rests the manual resetting button 10 protruding through the cover 2a. Insulating spacing bushes 11, 12, 13, 14 support the foregoing parts, the complete assembly being clamped to the base 2 by a nut 15 on the stud 1.

The switching member carries one contact 16 of the switch and a twin armature member 17 which ernbraces the magnet 18 held in the end of the plate 8. The fixed contact 20 of the switch is carried on a flexible blade 19 and is provided with a screw to enable adjustment to be made to the position of the twin armature relative to the magnet in the closed position of the switch.

An insulating push rod 21 carried by the free end of the bimetal strip 3 is arranged to push the spring switch lever 7 through the medium of an adjustable screw 22.

In magnetic snap action switches it is necessary that some resilient member be provided to store the thermal movement so that a gradually increasing force may finally overcome the pull of the magnet on the armature to open the switch contacts.

In this construction, as indicated in Fig. 2, the spring switch lever 7 consists of two parts, viz. a spring blade 23 clamped at one end in the switch pack and carrying at its other end one contact 16, the armature 17 and a second strip or tongue 25 riveted at 24 between the first blade and the armature and extending towards the clamped end of the blade 23. At a point near its end, and remote from its rivet, tongue 25 is tapped to carry a screw 22 adjustable in the tongue to contact the end of the push rod 21. Adjustment of this screw provides the means of setting the operating temperature of the switch. This adjusting screw is so p0- sitioned as to be approximately on the effective pivot line of the spring switch blade. Thermal movement of the bimetal operating element 3 moves the push rod 21 to press the screw 22 which is pushed upward storing the movement as a spring force in tongue 25 tending to open the contacts of the switch against the pull of the magnet on the armature. This movement gives a rolling action to the contact 16 on the fixed contact 20. When the switch is tripped in the position indicated in Fig. 3, the lower half of the twin armature 17 comes into close proximity to the magnet 18 the pull of which holds the switch open until it is reset by manual pressure on the button 10 which presses on the armature 17 and with it moves the switch blade 7 to the closed circuit position shown in Fig. l. In this position the attraction of the magnet 18 on the upper half of the armature 17 retains the switch in closed position until such attraction is overcome by the thermal movement of the bimetal operating element as described.

Tags 26 provide connection between the switch parts and terminals 27 fixed on the outside of the cover of the device.

I claim:

l. A magnetic snap action safety switch for automatically switching oil an electrically heated appliance on reaching excessive temperature, comprising a magnet, a resilient switch lever, said resilient switch lever carrying one switch contact and a U-shaped armature with its limbs embracing the magnet and with one limb of the armature in normal condition nearer to the magnet than the other, a flexible blade carrying a second contact of the switch, a thermally sensitive bimetal member located in a position to be influenced by the temperature of the appliance, movement transmitting means between the bimetal member and the resilient switch lever, said bimetal member being adapted on the rise of temperature of the appliance to push the movement transmitting means and in turn the resilient switch lever with its contact clear of the second contact to open the switch and to bring the other limb of the armature nearer to the magnet of the switch and out of the influence of any subsequent movement of the bimetal member, and manually operable means for restoring the position of the limbs of the armature in relation to the magnet and for remaking the contacts of the switch.

2. A magnetic snap action safety switch for automatically switching oil an electrically heated appliance on reaching excessive temperature, comprising a magnet, a resilient switch lever, said resilient switch lever carrying one switch contact and a U-shaped armature with its limbs embracing the magnet and with one limb of the armature in normal condition nearer to the magnet than the other, a flexible blade carrying a second contact of the switch, a thermally sensitive bimetal member located in a position to be influenced by the temperature of the appliance, a push rod attached at one end to the bimetal member with its other end in the path of the resilient switch lever, said bimetal member being adapted on the rise of temperature of the appliance to push the push rod and the resilient switch lever with its contact clear of the second contact to open the switch and to bring the other limb of 4 the armalture iaiieen'er to the magbnet of the switch am; References Cited in the file of this patent out of t e in uence ofV any su sequent movement o the bimetal member, and manually operable means for UNITED STATES PATENTS restoring the position of the limbs of the armature 111 2,385,887 Shaw Oct. 2, 1945 relation to the magnet and for remaking the contacts 5 2,500,704 Rennecamp Mar. 14, 1950 of the switch. 2,519,558 Flight et a1. Aug. 22, 1950 

